In each case, we asked the site to estimate the trade-in value for a phone in "excellent" or "like new" condition, with all of the original cords and packaging included.

Your mileage may vary, of course. Expect to earn a little less if your phone is in poor shape or missing any accessories. Also, these trade-in prices are likely to change day-to-day and even hour-to-hour. As demand goes down or supply goes up (like after the iPhone 4S gets into consumers hands), these trade-in values will probably drop. The best time to sell off your old iPhone is right now.